Peripheral artery disease (PAD) is a manifestation of systemic atherosclerosis, characterized by atherosclerotic blockages of the arteries supplying the legs. Claudication, defined as walking induced gait dysfunction and muscle pain, is the most common manifestation of PAD. Claudication affects 5% of Americans older than 55 years of age. Claudicating patients experience reduced mobility, reduced physical functioning, poor health outcomes, and increased risk for falls. Research in our laboratory has documented significant deficits in the ankle plantarflexors to generate normal torque and power during walking. Further, affected legs of patients with PAD demonstrate a muscle myopathy that prevents normal muscle function. While supervised exercise is effective for increasing the distance patients with PAD can walk, it does not generate ankle plantarflexor torque, or decrease stress on the leg muscles. An ankle- foot orthosis (AFO) is a device made of carbon-composite material that can offset ankle plantarflexor torque and power and decrease blood flow demand and muscular stress during walking. The spring-like properties of carbon composite AFOs allow energy storage at weight acceptance and return at the point of toe off. Our pilot work has shown that walking with an AFO immediately increases the initial and absolute walking distances in patients with PAD as much as pharmacotherapy for six months. This study will determine whether an AFO improves walking performance in patients with PAD from its first use. Additionally, the study will test walking performance after a three month AFO intervention and will examine the feasibility of this AFO intervention. The central hypothesis is that the AFO immediately improves walking performance by decreasing the energy cost of walking. Walking performance improvement following the three-month intervention is expected to be larger than that of first use due to improving the muscular function of patients' affected legs. Detailed measures of mechanisms related with walking performance, muscle contribution, physical activity, quality of life and how these mechanisms change after wearing the AFO for three months will provide the evidence required to implement an AFO therapy that will improve functional status and quality of life in individuals with PAD.